Prolactin Influence on Cytosol and Nuclear Androgen Receptors in the Ventral, Dorsal, and Lateral Lobes of the Rat Prostate*

PRL augments testosterone-mediated growth of the prostate in a permissive manner. To elucidate the mechanism of this hormonal interaction, the present study examined the effect of PRL on cytosol and nuclear androgen receptors in the three prostate lobes. Adult male Sprague-Dawley rats were castrated, given 5-mm Silastic implants of testosterone, and either grafted with two anterior pituitary glands under the kidney capsule or sham operated. Three weeks later, animals were killed, serum was collected for PRL and testosterone RIA, and the ventral, dorsal, and lateral prostate lobes were processed for either cytosol or nuclear androgen receptor quantitation. Pituitary grafts significantly elevated the serum PRL concentration and increased the weight and the content of protein and DNA of the lateral prostate lobe compared to control values. There was no effect on these parameters in the ventral or dorsal lobes. Androgen receptor levels and apparent distributions were different in the ventral, dorsal, and lateral lobes of control animals. Unoccupied and total cytosolic androgen receptors in the three separate prostate lobes were not significantly affected by the presence of the grafts. However, an elevated PRL concentration was associated with an increase (P less than 0.005) in nuclear androgen receptor content in the lateral lobe exclusively. The binding affinity was not altered by pituitary grafts in any of the lobes. These findings suggest that PRL promotes lateral prostatic growth by increasing nuclear androgen receptor levels in that tissue and, thus, optimizes its response to circulating testosterone.